SB XLVIII truly a showcase of powers

When the Broncos and Seahawks advanced to the Super Bowl, we football fans were given a rare gift: a meeting of what are (most likely) the two best teams in football on the game's biggest stage.

According to Pro-Football-Reference.com's Simple Rating System (SRS), Sunday's game will be just the sixth Super Bowl since the NFL-AFL merger to pit No. 1 and No. 2 from the regular-season rankings -- and the first time the top two teams have faced each other in more than a decade.

Here's a list of every Super Bowl in that group (the team's SRS is its average point margin, adjusted up or down according to its opponents' strength):

But all of those calculations don't necessarily prove the Broncos and Seahawks are the best teams in football. It's important to keep in mind that both squads have played only 18 games apiece in 2013, with their opponents representing a mere cross-section of the whole league. The NFL season is so short -- and the role of randomness so great -- that a team's performance may not reflect its true ability.

Fortunately, the Simple Rating System also has a mechanism to quantify the uncertainty in each team's rating (including playoff results). We can use this feature to compute the probability that any given team is truly the NFL's best. It can even tell us what the odds have been since the merger that the Super Bowl featured the league's two best teams. As it turns out, Sunday's game doesn't offer the greatest confidence that the two top teams are playing, but it comes pretty close.

Let's go to the list, starting with the Super Bowls for which we could be most certain involved the two true superpowers of the NFL:

1. Super Bowl XIII (1978 season) -- Dallas vs. Pittsburgh

Probability that they were the two best teams: 70.6 percent

Super Bowl XIII easily ranks first here, thanks to an NFL season where Pittsburgh and Dallas dominated the league all season. The Cowboys and Rams both went 12-4 in the NFC, but Dallas outscored opponents by 11 points per game, compared to Los Angeles' plus-4.4 differential. The Cowboys also crushed the Rams 28-0 in the conference championship game.

Meanwhile, nobody in the AFC was even close to the 14-2 Steelers, who cruised through the playoffs with a 67-15 scoring margin going into the Super Bowl. Statistically, there was only a 6 percent chance that any team other than Dallas or Pittsburgh had the best true SRS. The third most likely claimant to No. 1 was Miami, checking in with a paltry 3.5 percent probability.

2. Super Bowl XIX (1984) -- San Francisco vs. Miami

Probability that they were the two best teams: 54.2 percent

The 49ers were the class of the NFL in 1984, leading the league with a 15-1 record (the only loss coming to the Steelers on a missed field goal with seconds left on the clock) and logging a commanding plus-15.5 PPG differential. The Dolphins rode a record-setting Dan Marino performance to an AFC-best 14-2 mark during the regular season, then put up 38 points per game in wins over Seattle and Pittsburgh in the playoffs.